The prior art includes a number of different methods and apparatus for manufacturing flexible containers that are subsequently used to dispense pasty or viscous products such as skin lotions, toothpaste and shampoo. For example, U.S. Pat. No. 5,621,960; issued Apr. 22, 1998 to Kaminsiki; discloses a method and apparatus for applying a threaded closure to an inverted tube-type flexible container. The apparatus includes a rotatably mounted, belt-driven chuck mounted on an outer end of a radially extending arm of a rotatable indexed turret. The chuck includes axially downward extending lugs configured to engage recesses in the inverted base of a flexible tube and enabling the chuck to rotate the tube. The resulting tube rotation drives a threaded neck of the tube into an inverted threaded cap. To secure the cap against rotational movement, the cap is clamped between a semi-circular star wheel recess and an opposing semi-circular recess in a cylinder-driven, reciprocally mounted clamp. The star wheel is coaxially mounted on and rotatably indexes with the turret. Following this capping operation, the inverted base of the flexible tube is severed to provide an opening for a subsequent filling operation. Unfortunately, the amount of torque that can be applied to screw a flexible bottle into a threaded cap in this way is limited by the rigidity of the walls of the flexible bottle. Excessive torque will cause the bottle to twist and/or crush. This torque limit consequently limits both the speed at which the bottle can be screwed into the cap and the tightness of the cap on the bottle. In addition, even if a torque limiter is adjusted to apply an optimum amount of torque for a given wall thickness and/or rigidity, variations in wall thickness can result in an unacceptably high scrap rate.
Some machines that handle flexible containers use gas inflation to temporarily rigidify the containers. In some cases, such machines use gas inflation to enable the flexible containers to withstand forces typically applied during various labeling operations. For example, U.S. Pat. No. 5,259,912; issued Nov. 9, 1993 to Cline; discloses an apparatus for continuous in-line labeling of flexible walled bottles. The apparatus includes an air pulse station that directs pressurizing gas into the bottles. The gas inflates the bottles through uncapped mouths of the bottles and allows the bottles to resist compression as conveyor members compressively hold them and labeling machinery applies labels to the bottles. Bottle filling and capping occurs after inflation.
In at least one other flexible tube handling machine, gas inflation is used to form and hold the shape of flexible containers until the containers can be sealed. U.S. Pat. No. 4,136,502; issued Jan. 30, 1979 to Shore; discloses an inflater sealer machine that clamps the open upper portion of a flexible container, fills the container with a quantity of gas, then seals the upper portion closed. The gas pressure inflates the container into its desired shape then maintains that shape until the sealer machine seals it closed.
What is needed is a method for driving the threaded neck of a flexible container into a threaded closure without crushing or twisting the container. What is also needed is a closure-applying apparatus configured to accomplish this.